A two-dimensional echocardiographic particle image velocimetry (PIV) technique introduced in 2010 received much attention in clinical cardiology (Kheradvar, A, et al. (2010) “Echocardiographic particle image velocimetry: a novel technique for quantification of left ventricular blood voracity pattern” Journal of the American Society of Echocardiography 23(1): 86-94.
Particle image velocimetry (PIV) has been significantly advanced since its conception in early 1990s. With the advancement of imaging modalities, application of 2D PIV has far expanded into biology and medicine. One example is echocardiographic particle image velocimetry that is used for in vivo mapping of the flow inside the heart chambers, which have opaque boundaries. The current trend is to develop three-dimensional velocimetry techniques that take advantage of modern medical imaging tools.
The most commonly used velocimetry techniques to measure optical flows are based on tracing the particles in a fluid flow. Since early 1990s, several algorithms for particle tracking have been developed that are generally referred to particle image velocimetry (PIV). PIV techniques were originally developed based on the snapshots of two- or three-component velocity vector field on a planar cross section of the flow (Westerweel, J. et al. Annual Review of Fluid Mechanics, 2013 45(1): p. 409-436). PIV techniques are evolving with the advancement of software technology, and faster processors as well as technical improvements in imaging hardware. This facilitates the development of new enterprises for measuring the velocity over volumetric domains.
Some of the noteworthy three-dimensional PIV techniques are defocusing PIV (Pereira, F. and M. Gharib Meas Sci Technol., 2002. 13: p. 683-94), holographic PIV (Barnhart, D. H. et al. Applied Optics, 1994. 33(30): p. 7159-7170), Multi-Planar PIV (Falahatpisheh, A. et al. Experiments in fluids, 2014. 55(11): p. 1-15), and Tomographic PIV (Elsinga, G. E., et al. Experiments in Fluids, 2006. 41(6): p. 933-947). The accuracy of the measurement for each 3D PIV method depends on many experimental parameters, particularly on the particle image density, the volume depth, and the type and number of acquisition devices, which make quantitative validation difficult. So far, no 3D PIV challenge has been defined to compare the accuracy of different methods, as previously described for 2D PIV techniques (Stanislas, M., et al. Experiments in Fluids, 2008. 45(1): p. 27-71). However, while the three-dimensional velocity in a particular flow situation is unique, it is anticipated that each 3D PIV technique reports a slightly different vector field. Therefore, there is a need for a platform to systematically validate these methods.